CVE-2015-4645 in squashfs
Summary
by MITRE
Integer overflow in the read_fragment_table_4 function in unsquash-4.c in Squashfs and sasquatch allows remote attackers to cause a denial of service (application crash) via a crafted input, which triggers a stack-based buffer overflow.
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Analysis
by VulDB Data Team • 09/09/2020
The vulnerability identified as CVE-2015-4645 represents a critical integer overflow condition within the squashfs and sasquatch file system utilities, specifically affecting the read_fragment_table_4 function in unsquash-4.c. This flaw manifests when processing specially crafted squashfs image files, creating a scenario where an attacker can manipulate the input data to trigger unexpected behavior in the application. The vulnerability falls under the category of software defects that can lead to memory corruption issues, making it particularly dangerous in environments where untrusted input is processed without proper validation. The integer overflow occurs during the parsing of fragment table data structures, which are used to manage file fragments within squashfs compressed file systems. When the application attempts to calculate buffer sizes based on malformed input values, the arithmetic operation results in an integer overflow that subsequently leads to a stack-based buffer overflow condition. This type of vulnerability is classified as a CWE-190 - Integer Overflow or Wraparound, which is a well-documented weakness in software security that often leads to memory corruption and potential arbitrary code execution scenarios.
The operational impact of this vulnerability extends beyond simple denial of service, as the stack-based buffer overflow can potentially be exploited to execute arbitrary code on the target system. When the application processes a maliciously crafted squashfs image, the overflow corrupts the stack memory layout, which can result in application crashes or, in more sophisticated attack scenarios, allow attackers to overwrite critical program execution data. The vulnerability affects both squashfs and sasquatch utilities, indicating a broader impact across related file system tools that implement similar parsing logic for squashfs format handling. Attackers can leverage this weakness by preparing a specially crafted squashfs image file that contains malformed fragment table entries, causing the application to allocate insufficient buffer space for processing the data. The attack vector is particularly concerning because it requires only a single malicious input file to trigger the vulnerability, making it suitable for remote exploitation scenarios where attackers can deliver the payload through various means such as web downloads, email attachments, or file sharing systems. This vulnerability aligns with ATT&CK technique T1203 - Exploitation for Client Execution, where adversaries leverage software vulnerabilities to execute malicious code on target systems.
Mitigation strategies for CVE-2015-4645 should focus on both immediate patching and defensive programming measures. Organizations should prioritize updating their squashfs and sasquatch implementations to versions that address the integer overflow condition in the read_fragment_table_4 function, which typically involves implementing proper input validation and boundary checking for all arithmetic operations involving buffer size calculations. The fix should include bounds checking mechanisms that prevent integer overflows from occurring during fragment table processing, ensuring that calculated buffer sizes remain within reasonable limits. Additionally, implementing proper input sanitization techniques can help prevent malformed data from reaching the vulnerable parsing functions, including validating all fragment table entries before processing them. Security measures should also include deploying application whitelisting solutions that restrict execution of untrusted squashfs processing tools and implementing network-based controls that scan for and block potentially malicious squashfs files. The vulnerability demonstrates the importance of proper software security practices, particularly in handling file format parsing operations where integer arithmetic is involved, and highlights the need for comprehensive testing including fuzzing techniques to identify similar issues in other file system utilities. Organizations should also consider implementing runtime protections such as stack canaries or address space layout randomization to make exploitation more difficult even if the vulnerability is present in the system.